Container for corrosive liquids



June 1964 J. L. FARELL ETAL 3,135,420

CONTAINER FOR CORROSIVE LIQUIDS Filed June 22, 1962 2 Sheets-Sheet lINVENTORS JACK L. FARELL CHARLES A. HOMSY ATTORNEY J1me 1954 J. 1..FARELL ETAL CONTAINER FOR CORROSIVE LIQUIDS Filed June 22, 1962 FIG.4

BY flwza Q 2 Sheets-Sheet 2 INVENTORS JACK L. FARE L L CHARLES A. HOMSYA ORNEY United States Patent This invention relates to containers forcorrosive fluids. The handling of corrosive fluids often presentsproblems in chemical processes because of the deleterious effect whichsuch ,rnaterials have on metal equipment. This deterioration ofequipment may be accompanied by an additional problem, namely,contamination of the process steams by the products of the interactionof metal and the corrosive agent. These dilficulties have been overcomein part through the use of more costly metals having greater chemicalresistance to the conesive materials." Even more recently, it has beendiscovered that metal equipment can be shielded by means of liners orcovers fabricated from high polymers which are substantially chemicallyinert to the corrosive substance. As a result of the aforesaiddevelopments, corrosi'on problems have beenreduced sharply, although noteliminated completely. For example, because of the tendency of corrosiveagents to diffuse through polymeric barriers, a chemical attack of arnetal exterior structure still may occur after diffusion of the agentthrough the liner. Furthermore, there may be either a chemical orsolvent attack on the cement or adhesive normally used to bond thepolymeric liner to the outer structure. The bonding agent may beattacked not only by'the corrosive agent diffusing through the liner,but by other relatively inert materials, for example, moisture. Althoughthis difiiculty may be circumvented by fabricating the container solelyfrom the inert polymerthus removing the need for an exterior structureand a bonding agent, such a remedy usuallyis precluded because of eitherthe inherent lack of self-supporting rigidity in the polymer selected orthe high cost of the quantity of polymer needed to achieve self-support.A still further difficulty often encountered when employing polymericliners is blistering of the exterior surface of the.

liner, particularly at temperatures above 100 C. Such blistering, theorigin of which is unknown tends to shorten the life of the liner.

It is an object of the present invention to provide a new and usefulcontainer for corrosive fluids. Another object is to provide-a containerwhich utilizes a high polymer membrane or interior member between thematerial to be contained and an exterior member or outer wall. on theaforesaid polymer membrane. A still further object is to hold saidpolymer membrane in place within the outer member without the use of acement or bonding agent. Other objects will become apparent hereinafter.

The objects of the invention are achieved by means of a dual-walledcontainer comprising an exterior, rigid, supporting, enclosing member orwall containing therein an interior, supported enclosing member or wallhaving a loading or discharging passage leading therefrom through saidouter member. The inner wall or liner is fabricated from a high polymerwhich is essentially inert to the corrosive fluid to be containedtherein. Furthermore, the liner is substantially isolated from the outerwall by a vapor space through which flows an inert gas stream to purgeout any fluid material diffusing through the inner polymer wall. Theinner polymer membrane may be held in place and supported by a varietyof means. If the inner polymer wall exhibits sufficient rigid- A furtherobject is to prevent blister formation.

3,135,420 Patented June 2, 1964 'ice ity to be self-supporting, it. mayhave affixed to its outer side suitably positioned studs which are heldin place on the outer wall. The studs may be affixed to the inner wall,for example, by heat-sealing, or they may be formed concurrently duringthe wall fabrication step. The stud may be threaded on one end, thethreaded end being extended through the outer vessel wall and suitablyheld in place. A metal rivet running through the inner wall and havingits head protectively coated with an organic polymer, likewise, may beused to hold the liner in place.

. Variations of the above, particularly as to the number and location ofthe studs or rivets, may be employed.

' For example, the vapor "space between the inner and outer-walls may bemaintained under a high inert gas pressure to 'aid in providing supportfor the fluid-filled inner member. In this case, the positive pressureof the inert gas may retard the diffusion of the corrosive agent throughthe inner wall. Especially suitable in this invenare parallel with eachother, there may be a series of.

parallel" ribs which is angular with one or'more other series ofparallelribs depending upon the shape of the container. For example, theseries of parallel ribs in the end sections of a cylindrical tank may beangular to a series of parallel ribs in the side. Furthermore, in aspherical container the ribs may become non-parallel as they converge atthe poles. A particularly advantageous feature of using the ribbedconstruction is that the polymeric innerwall may be fabricated fromsheetinghaving the ribs directly incorporated therein. Ribbed sheetingmay be formed by standard extrusion techniques using a notched die tointroduce the ribs, after which the ribbed sheet may be shaped toprovide .the interior member or wall of the container. For mostapplications, the nominal polymer wall thickness, i.e. the Wallthickness exclusive of ribs or support means, may be 0.01 to 0.10 inch.When using ribbed liners, the outer wall may contain appropriatelyspaced ridges or indentations which serve to hold the liner in place.Peripheral spacing rings or strips which may be fabricated independentlyand aifixed either to the inner or the outer wall, also, may be used toprovide the same effect as the ribbed wall, namely, to substantiallyisolate the inner and outer walls while providing support for the innerwall. A still further variation in the present invention may be realizedby filling the space between the inner and outer walls with a highlypermeable inert material which provides structural support withoutmaterially impeding the flow of purge gas. Asbestos may be cited as anexample of such a porous material. Regardless of which of the abovestructural variations are employed, an essential aspect of the inventionis the positive flow of inert gas which purges out any material which isentrapped between the walls after diifusing through the polymeric innerwall.

Although it is preferable to minimize contact between the inner andouter walls of the container, structural features must of necessityinclude contact between the two at the studs, ribs, and the like becauseof the need for supporting and positioning the interior member. On theother hand, in order to maintain a purge flow adequate flow may suifice.

members. A particularly useful range of percentage purge space is 70 to75%. Conversely, it may be stated that the support means can occupy 3 to50%, and preferably 25 to 30%, of the total voulme between the inner andouter members. When the ribbed-type inner wall is employed, thispercentage free volume may be achieved by adjusting the ribbed spacing,i.e. the distance between adjacent ribs on the inner wall, to 0.05 to0.50 inch and the rib height, equal to the distance between the Walls atthe non-ribbed surface of the inner wall by a path normal to both walls,to 0.01 to 0.30 inch. The rib itself may have various shapes dependingupon the method of fabrication. For example, the plain surfaces formingits sides may meet the inner and outer walls normal to their surfaces.The ribs, also, may be saw-tooth or truncated triangular in crosssection, normally having their greatest thickness at the juncture withthe inner wall.

In order to supply and maintain a positive flow of inert gas between thedual walls of the above-described container, suitable inlet and outletvalves must be provided. Likewise, baffles or a deflecting means must beinstalled between the inner and outer members to deflect the gas andensure effective purging. When the ribbed inner wall construction isemployed, a suitable manifold must be included so as to divert the flowof gas uniformly to all channels between the ribs. The flow of purge gasmay be varied depending upon the rate at which the corrosive materialbeing contained diffuses through the polymeric Wall. When this diffusionrate is low, intermittent gas Suitable monitors may be installed at thepurge gas exit port to determine optimum flow rate. The purge gaspreferably employed may be any gas which. is inert to the materials ofconstruction as well as to the agent being removed by the purge. Formost operations dry air or nitrogen is used because of its readyavailability.

The inner wall in the present invention may be fabricated from anyorganic polymer which is resistant to the corrosive agent beingcontained therein. Particularly useful are film-forming polymers, andespecially those which have a high degree of rigidity. As examples ofpolymers useful herein may be cited the hydrocarbon polymers, especiallyhigh density polyethylene, polypropylene, polystyrene, and the like, thehalogenated hydrocarbon polymers, such as polyvinyl chloride, thefluorinated hydrocarbon polymers, and the like, the polycarbonates,polyoxymethylenes, polyamides, and the chlorinated polyethers. Thefluorinated hydrocarbon polymers are generally the most useful becauseof their inherent chemical inertness.

Polymers prepared from tetrafluoroethylene, tetrafluoro ethylene andhexafiuoropropylene, vinylidene fluoride and chlorotrifluoroethylene arerepresentative of this type of polymer.

The outer wall of the dual-walled container frequently is fabricatedfrom a metal which provides both rigidity and mechanical strength. Sincethe use of expensive corrosion-resistant metals is unnecessary as aresult of the present invention, greater latitude in the selection ofthe material used for the outer wall has been achieved.- For many uses,the outer wall may be constructed from a polymeric material whichpossesses the requisite structural characteristics of an outer orprotective member. Moreover, the selection of a polymeric outer wall isfurther enhanced because of the absence of any necessity to consider itschemical reactivity with the corrosive agent being contained. Especiallysuitable as polymeric outer walls are the thermoplastic resins such asthe hydrocarbon polymers. e.g., polyethylene, particularly thehigh-density variety, polypropylene, polystyrene and copolymers ofstyrene, the polyoxymethylenes, polycarbonates, polyamides, and thelike, as' well as thermosetting resins and reinforced plastics.

The term container as employed herein refers to a structure which isused for the confinement and retention of a fluid within a given spaciallimitation and necessarily includes structures for confining not onlyessentially stagnant fluids but moving fluids as well. Containers usefulin the latter application include pipe and tubing used in transferringfluid process streams, raw materials, products, and the like. Thecontainers described herein may be employed for confining eitherstationary or flowing fluids over a wide range of temperatures, thetemperature being limited only by the ability of the polymeric wall orWalls to withstand operating conditions. Heating or cooling of thecontainer may be effected by means of an external source whichconcurrently heats or cools the container and the purge gas. The heatingor cooling means, likewise, may be incorporated within the space betweenthe walls of the container. Finally, the temperature of the containermay be controlled by means of independently heated or cooled purge gas.The free space between the inner and outer members may provide anadditional feature in the present invention by serving as a thermalbarrier between the.

corrosive material being environment.

A particularly preferred'embodiment of the present invention is depictedin FIGURES 1 to 7.

FIG. 1 is an elevation view of a kettle or container with a portion ofthe exterior wall broken away to expose the interior member.

FIGURE 2 is a transverse sectional view along line 2-2 of FIGURE 1showing the exterior and interior members.

FIGURE 3 is an enlarged fragmental transverse sectional view along line33 of FIGURE 1 showing constructional details of the head and baseportions of the container.

FIGURE 4 is an enlarged fragmental sectional view of the ribbed sheetingforming the interior member of the container.

FIGURE 5 is an enlarged fragmental perspective view showing the ribbedsheeting forming the side and bottom of the interior member of the baseportion of the container.

FIGURE 6 is an enlarged fragmental perspective view showing the ribbedsheeting forming the side and top of the interior member of the base andhead portions of the container and, also, showing the overlap at theflanges of the base and head portions of the ribbed sheeting forming theinterior member of the container.

FIGURE 7 is a vertical enlarged fragmental view showing the ribbedsheeting forming the head liner portion of the interior member of thecontainer. A

More specifically, FIGURES 1 and 3 show a kettle or container having acylindrical metal exterior member which is split at the top so as toprovide a removable head 1 which may be afiixed to the base 2 of thecontainer by a plurality of bolts 3, inserted through holes suitablypositioned along the flanges of the head and the base, to effectsealing. A ribbed-type interior member is utilized, with the interiormember being fabricated from ribbed sheeting, FIGURE 4, which is formedfrom a tetrafluoroethylene-hexafluoropropylene copolymer. The sheetingis vacuum formed to the desired shape to fit the base and head of thecontainer. If preferred, the liner 4 for the base 2 of the container maybe formed by joining together, using conventional melt bondingtechniques, sections of sheeting corresponding to the side, bottom andflange of the liner. The liner 5 for the head 1 may be similarly formed.A section is cut from each of the parallel ribs in both liners 4, 5 toform a crosschannel or manifold 6 so as. to permit uniform urging of thesystem by providing equidistant paths of gas flow between the inlet andoutlet purge gas ports 7. FIGURE 2 depicts the interior and exteriormembers with the parallel longitudinal channels 8 through which passesthe purge gas, while FIGURE 5 shows a portion of the side and bottom ofthe base liner 4. FIGURE 6 depicts the overlap of the flanges of thebase liner 4 and the head contained and the external V liner 5 withappropriate spacing washers 9, and FIGURE 7, the head liner 5 withparallel channels 8, the crosschannel or manifold 6 and the spacingwasher 9.

A dual-walled container of the aforesaid description is filled with 10weight percent hydrochloric acid, then heated to and maintained at 200F. for 10 days. During this time a dry air purge gas is passed betweenthe interior and exterior members of the vessel ata rate of 75 cc. perminute (corrected to standard temperature and pressure). After 10 daysthe vessel is cooled and the acid is removed. The metal exterior memberbeneath the liner is free from any evidence of chemical attack and theacid is still water white. Furthermore, the outside of the polymericliner is free of blisters. A control experiment run at the sameconditions without the liner results in serious corrosion and pitting ofthe metal exterior member as'well as discoloration and contamination ofthe acid. A

second control experiment run with the polymeric liner but without thepurge gas results in less corrosion to the metal'shell than without theliner, but the outer wall of the liner is blistered.

We claim:

l; A container for retaining fluid materials, said container comprisinga supporting, rigid exterior member, an interior member fabricated froman organic polymer and having a passage leading therefrom which providesa means of conducting said fluid materials through said exterior member,a plurality of support means for maintain ing said interior member inspaced relation to and separated from said supporting exterior member,said support means occupying 3 to 50% of the spaced volume between saidinterior and exterior members, a means for introducing a purgegasbetween said interior and exterior members, a deflection means fordiverting said purge gas uniformly between said interior and exterior Vmembers and means for removing said purge gas.

2. The container of claim 1 wherein said organic polymeric interiormemberis fabricated from a ribbed film having a nominal thickness of0.01 to 0.10 inch-a wall distance between ribs of 0.05 to 0.50 inch anda rib height of 0.01 to 0.30 inch, said organic polymer being selectedfrom the group consisting of hydrocarbon polymers,

6. halogenated hydrocarbon polymers, polycarbonates, polyamides,polyoxymethylenes and chlorinated polyethers.

3. The container of claim 1 wherein said organic polymeric interiormember is fabricated from a fluorinated hydrocarbon polymer. I a

4. The container of claim 1 wherein said plurality of support means arepredominantly parallel-spaced ribs 0.01 to 0.30 inch in height andextending peripherally about said interior member with an interior walldistance between ribs of 0.05 to 0.50 inch.

5. A method for containing corrosive chemical fluids, said methodcomprising introducing said corrosive fluid into an enclosing, organicpolymeric, interior member through a passage leading therefrom through arigid, exterior, supporting member, said exterior member having a purgegas entrance port and a purge gas exit port, said I interior memberbeing separated from and held in spaced relation to said exterior memberby a plurality of support means, said support means occupying 3 to 50%of the space volume between said interior and exterior members, passingan inert purge gas through said gas entrance port and removing saidpurge gas through said gas exit port.

interior member with an interior Wall distance between ribs of 0.05 to0.50 inch.

References Cited in the file of this patent -UNITED STATES PATENTS2,638,338 Williams May 12,1953 2,772,860 Nelson Dec. 4, 1956 3,068,561

Jones Dec, 18, 1962 wherein said organic poly-

1. A CONTAINER FOR RETAINING FLUID MATERIALS, SAID CONTAINER COMPRISINGA SUPPORTING, RIGID EXTERIOR MEMBER, AN INTERIOR MEMBER FABRICATED FROMAN ORGANIC POLYMER AND HAVING A PASSAGE LEADING THEREFROM WHICH PROVIDESA MEANS OF CONDUCTING SAID FLUID MATERIALS THROUGH SAID EXTERIOR MEMBER,A PLURALITY OF SUPPORT MEANS FOR MAINTAINING SAID INTERIOR MEMBER INSPACED RELATION TO AND SEPARATED FROM SAID SUPPORTING EXTERIOR MEMBER,SAID SUPPORT MEANS OCCUPYING 3 TO 50% OF THE SPACED VOLUME BETWEEN SAIDINTERIOR AND EXTERIOR MEMBERS, A MEANS FOR INTRODUCING A PURGE GASBETWEEN SAID INTERIOR AND EXTERIOR MEMBERS, A DEFLECTION MEANS FORDIVERTING SAID PURGE GAS UNIFORMLY BETWEEN SAID INTERIOR AND EXTERIORMEMBERS AND MEANS FOR REMOVING SAID PURGE GAS.